WHILE STARTING LOAD FACE ROUND, PRILL HOSE WAS INSERTEC INTO HOLE. VALVE OPERATOR TURNED ON VALVE TO START PRILL INTO HOSE. THE AIR BLEW HOSE OUT OF THE HOLE. HOSE WHIPPED AND BLEW PRILL IN OPERATOR'S EYES AND BLOW OFF HIS HARD HAT AND GLASSES. VALVE OPERATOR WAS SLOW IN TURNING OFF VALVE.